The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
With a rapid propagation of smart phones and continuing increases in the number of content providers using smart phones, there is a growing tendency toward an increase in traffic of mobile communication networks. The inventor(s) has experienced that this may often cause the deterioration of service quality due to a decrease in a transmission rate of contents such as videos, audios, images, applications, and the like.
Meanwhile, a recent growth of content transmission technology allows transmission of large-capacity files in online video services such as VOD (Video On Demand) or live streaming, in music streaming services, and in file upload and download. Thus, a variety of services for delivering large-capacity contents are provided.
Normally such content providing services tend to deliver redundant contents to users in the same domain or the same radio coverage even though the frequency of content delivery depends on its popularity. The inventor(s) has noted that as various content providing services are widely used today, transmission of redundant contents occupies an increasing part of network traffic.
In a situation that network traffic sharply increases due to transmission of large-capacity contents, the inventor(s) has experienced that transmission of redundant contents further increases a traffic load of the communication network. In view of this, the inventor(s) has noted that a CDN (Content Delivery Network) service is used to stably deliver various types of contents such as movies, music video, and the like to end-users. In the CDN service, replicas of contents are stored in a plurality of local cache servers distributed in a network. A load balancer, also referred to as a GLB (Global Load Balance) server, selects an optimal cache server among the local cache servers, and the selected cache server delivers requested content to a user terminal.
This CDN architecture provides a solution to obviate several problems including data loss, bottlenecks, reduced transmission rate, network instability such as discontinuous data transmission, and the like.
In the CDN service, content caching technology is used for selectively caching contents in a plurality of local caching devices distributed in a network. Content caching should consider the size of a storage space in a local caching device, the time required to determine whether requested content is cached in the local caching device, and a cache hit rate that indicates a percentage that the requested contents are contained in the local caching device.
Particularly, in case of adapted content providing techniques (e.g., HTTP Live Streaming (HLS)) to transmit content by varying its resolution according to link quality or device performance, content is divided into a plurality of chunks and transmitted by the chunks. Therefore, if it is determined on the basis of parts of content whether the content is cached, service efficiency may be lowered due to a small amount of data transmitted from a local caching device to a user terminal. Additionally, some adapted content providing techniques periodically change an encryption key of content. If such an encryption key is changed, content data is changed through encryption in spite of having the same URL, and hence it is impossible to determine on the basis of URL whether the content is cached.